The excellent mechanical properties (particularly tensile strength and elongation) of commercially-available polyether-, polyester-, polycarbonate-, and polysiloxane-based polyurethanes (PUs) are largely due to their phase-separated micromorphology (precise arrangement of hard and soft segments) and extensive H bonding between —NH— donors and —C═O— acceptors in the hard segments. Polyisobutylene-based PUs (PIB-PUs), however, exhibit lesser mechanical properties than conventional PUs mainly because insufficient stress transfer between the highly segregated polar hard and apolar soft domains, and, importantly, insufficient H bonding between different segments.
A further fundamental difference between typical (commercially available) polyether-based PUs on the one hand, and PIS-based PUs on the other hand, is in respect to hydrolytic-oxidative-biological resistance: While the conventional polyether-based PUs are vulnerable to hydrolytic and oxidative damage (mainly on account of the many —CH2—O— linkages they contain in the soft segment), PIB-PUs are chemically resistant as their soft segments contains only of highly stable —CH2—C(CH3)2— units (See, Kennedy J. P, Ivan B., Designed Polymers by Carbocationic Macromolecular Engineering: Theory and Practice; Oxford University Press, New York, 1992, the disclosure of which is incorporated herein by reference in its entirety). The synthesis, characterization and properties of hydrolytically-oxidatively resistant PIS-PUs have been described and discussed together with the science and practical significance of their chemical stability/inertness (see, e.g., J. P. Kennedy, G. Erdodi, S. Jewrajka WO2010039986A1, J. P. Kennedy, G. Erdodi, J. Kang WO2011060161A1, Toth, K., Nugay, N. and Kennedy, J. P. (2015), J. Polym. Sci. Part A: Polym. Chem. 2015, xx, xxx, doi:10.1002/pola.27804, Erdodi, G.; Kang, J.; Kennedy, J. P. J Polym Sci Part A: Polym Chem 2010, 48, 2361-2371 and other parts of the series, the disclosures of which is incorporat3ed herein by reference in their entirety).
It is also well known that polyureas are typically stronger (exhibit higher tensile stresses) than polyurethanes because of the presence of stronger bifurcated H bonds in the former. FIGS. 1A-B show the structures of H bonds in polyurethanes (carbamates) (FIG. 1A) and polyureas (FIG. 1B).
The processibility of polyurethanes and polyureas is likewise fundamentally different. While polyurethanes are desirably melt processible, polyureas, on account of strong bifurcated H bonds, do not melt but degrade before melting. As a result, polyureas can only be solution processed by using strongly H-accepting environmentally objectionable solvents, (i.e., dimethyl acetamide, dimethyl formamide). One well known example of such a method is the dry spinning of spandex polyurea fibers from dimethyl formamide. In view of the use of noxious solvents, solution processibility of polyureas is costly, cumbersome, and environmentally unfriendly.
Accordingly, there is a need in the art for a PU that has enhanced mechanical properties, while maintaining the melt processibility of PUs in general and thermoplastic elastomeric PUs in particular.